Use of
Potassium Permanganate to
Control External Infections of Ornamental FishBy:Ruth Francis-Floyd and RuthEllen Klinger

Many disease problems of ornamental fish begin as external infections.
If uncontrolled, the infections may become systemic, resulting in death of
the fish. Correct use of potassium permanganate can effectively control
many bacterial, parasitic and fungal agents before systemic infections
become established, often eliminating the need for antibiotic therapy. The
fish owner saves money because use of expensive antibiotics is decreased,
thereby decreasing the incidence of resistant bacterial strains. In the
ornamental trade, correct use of potassium permanganate at the onset of an
infection can also speed the movement of fish as they do not need to be
held for lengthy (often 10-14 day) antibiotic treatments.

What is Potassium Permanganate?

Potassium permanganate (KMnO 4 ) is an oxidizing agent that has
been used for many years in aquaculture. It is also used in water
conditioning systems and in the plumbing industry. As an oxidizer, it is
able to chemically "burn up" organic material. This includes
undesirable organic matter such as bacteria, parasites, and fungus, as
well as desirable material such as gill tissue and mucus. Because the
chemical cannot distinguish between desirable and undesirable organic
matter, it is up to the individual to use the chemical in a manner that
results in maximum benefit and minimum harm to treated fish.

Color Change Associated with Potassium Permanganate Use

When potassium permanganate is active (in its unoxidized form), treated
water turns a pinkish-purple color. As the chemical is
"deactivated" (by oxidizing organic material), the water color
changes to yellow or muddy brown. This color change is an important tool
when monitoring chemical treatment (discussed below); however, this may
make potassium permanganate undesirable for use in display tanks,
exhibits, or ornamental ponds. As with many chemicals used in water,
potassium permanganate is harmful to plants and invertebrates.

Use of Potassium Permanganate

For most fish, potassium permanganate can be administered at a
concentration of 2 mg/L as a long-term bath (4-hour minimum) in fresh
water or salt water systems. Potassium permanganate is also reasonably
safe to use in recirculating systems and has minimal impact on biofilters
when used at 2 mg/L. Treated water should retain the purple coloration for
at least 4 hours. Some fish, including certain Lake Malawi cichlids, are
sensitive to potassium permanganate and lower concentrations (1 mg/L) may
be safer. The fish owner can determine species sensitivity by observing
the behavior of the fish during treatment. This is especially important
when treating a species for the first time. If fish react adversely,
immediate action (such as diluting the chemical with fresh water) can be
taken.

Because potassium permanganate is deactivated by organic matter, it may
be necessary to increase the amount added to ponds or other systems where
organic material has been allowed to accumulate. A safe way of
accomplishing this is to add potassium permanganate to the system in 2
mg/L increments. If water color changes from purple to brown in less than
4 hours from the start of the first treatment, an additional 2 mg/L should
be added. If a total application of 6 mg/L potassium permanganate does not
result in maintenance of the purple color for at least four hours, the
system really should be cleaned. Most of the organisms that are treated
with potassium permanganate thrive in an organically rich environment, and
therefore improved sanitation can have a tremendous impact on treatment
efficacy.

Potassium permanganate can also be used as a short-term bath at
concentrations of 10 mg/L for 30 minutes. At this concentration, careful
observation of fish is mandatory to avoid mortality. This is a convenient
treatment when fish are being removed from ponds and brought into
buildings for sorting and shipping. Following a potassium permanganate
treatment with a low concentration (0.02-1.0%) of salt (sodium chloride)
as a semipermanent treatment for several days or weeks (depending on
species treated), can be beneficial. This combination is particularly
effective in minimizing Columnaris infections after handling fish.

Potassium permanganate can be used as a surface disinfectant at
concentrations of 10 (30-60 minutes contact time) to 500 mg/L (30 seconds
contact time) in a fish room or hatchery, however, quaternary ammonium
compounds are better suited to this purpose. Potassium permanganate will
kill bacterial, fungal and many parasitic agents, but it is not viricidal.

Frequency of Treatment

As mentioned above, potassium permanganate is an indiscriminate oxidizer,
and as such, can burn gill tissue and mucus of treated fish if too much
chemical is applied. A good rule of thumb to prevent excessive damage to
fish is to avoid treating them with potassium permanganate more often than
once a week. If a chemical treatment is needed for a condition that
requires more frequent application, such as treatment for an outbreak of
"Ich" ( Ichthyopthirius multifilis), potassium permanganate is not a good choice.

Treatment Failure

Poor efficacy following use of potassium permanganate is usually caused by
one of three factors: (1) incorrect or incomplete diagnosis; (2) incorrect
calculation or measurement of amount of chemical needed; and (3) excessive
organic material in the system resulting in rapid degradation of the
chemical. Any time treatment failure occurs, sick fish should be submitted
to a diagnostic laboratory for an accurate diagnosis. Volume of the water
treated, accuracy of calculations to determine treatment rate, and
accurate measurement (by weight) of chemical used are essential for
delivery of an appropriate chemical dose. As mentioned above, an excessive
amount of organic matter in the system will result in rapid deactivation
of potassium permanganate, and therefore contact time with active chemical
will be inadequate for effective treatment. This is often a problem in
heavily stocked ponds.

Determining the Amount of Potassium Permanganate to Use

To calculate the amount of chemical required, a simple formula can be
used:

Amount of Chemical = Volume x Conversion Factor x Treatment Rate

If the pond or tank volume is measured in gallons, the conversion
factor is 0.0038 and the answer will be given in grams (see Table
1 for other conversion factors). For a treatment rate of 2 mg/L, this
formula would be:

Grams of Chemical = Gallons Treated x 0.0038 x 2 mg/L

Therefore, to treat a 250-gallon vat, the grams of potassium
permanganate needed are:

Grams needed = (250 gal) x (0.0038) x (2 mg/L)

= 1.9 grams

An inexpensive gram scale can be obtained by purchasing a dietary scale
at your local grocery store or pharmacy. One level teaspoon of potassium
permanganate weighs about 7.0 grams.

Use of a Stock Solution

An alternative method of measuring potassium permanganate is to mix a
stock solution. A stock solution is a concentrated solution of chemical
from which small amounts can be taken to treat tanks as needed. This is
useful when either multiple tanks or multiple treatments are needed. An
easy way to make up a stock solution for potassium permanganate is to
purchase a one-gallon bottle of distilled water, weigh 285 grams of
potassium permanganate, add it to the solution, and mix thoroughly. This
stock solution will deliver a dose of 1 mg/L when delivered at a rate of
one drop per gallon. Therefore, to achieve the desired concentration of 2
mg/L, the stock solution can be delivered at a rate of 2 drops per gallon.
The stock solution should be stored in a cool, dark area and be replaced
annually.

When treating larger systems, it is useful to remember that 20 drops
are equal to one milliliter (ml), or one cubic centimeter (cc) if
measuring the liquid with a syringe. Therefore, one ml of stock solution
will treat ten gallons of water with a concentration of 2 mg/L.

Safety Precautions When Handling Potassium Permanganate

Potassium permanganate is fairly safe to handle, however, all chemicals
should be treated with respect. Potassium permanganate will easily stain
clothing and skin. Brown discoloration of skin is not painful, but it may
be unsightly and takes several days to disappear. Brown stains to clothing
can be permanent. Protective gloves and clothing are recommended when
handling potassium permanganate.

Fish farmers and aquarists do occasionally mix chemicals. It is
important that formalin and potassium permanganate are NEVER mixed
as the combination can be explosive.

Summary

Potassium permanganate is an oxidizer which can be used to
"disinfect" the external surfaces of fish. It effectively
removes most external parasites, as well as fungal and bacterial agents.
Most fish can be treated by prolonged immersion in a 2 mg/L potassium
permanganate solution (water must retain a purple color for at least 4
hours), although some species (i.e., Malawi cichlids) seem to be sensitive
to it and may not tolerate a full strength (2 mg/L) bath. Because of its
harsh oxidizing properties, potassium permanganate should not be applied
to fish more frequently than once per week or mortality may result. It is
safe to use in marine and recirculating systems at 2 mg/L. Potassium
permanganate can stain skin and clothing so care is suggested when
handling it. The chemical should never be mixed directly with formalin as
an explosion or fire could result.